1. Field of the Invention
The present invention relates to an electronic circuit with an outer shielding and at least an inner shielding within the outer shielding for preventing the electronic components of the electronic circuit from affecting one another.
2. Description of the Related Art
Electronic circuits having a shielding are generally known and customary in technology such as, for example, in motor vehicles for vehicle application apparatus. The shielding protects the electronic components of the electronic circuit against external electromagnetic influence and prevents electromagnetic waves from irradiating outwards from the electronic circuit so the electronic circuit does not disrupt any external electronic devices. Electronic circuits often contain electronic components which may affect one another. For this reason, these circuits require an inner shielding of individual components within the outer shielding of the entire electronic circuit. If the inner shielding is provided within the outer shielding, the conduct of the heat of the electronic components which are doubly shielded in this way causes difficulties. The internal shielding may be connected to the external shielding with thermally conductive rubber so that the heat passing into the internal shielding flows into the outer shielding via the thermally conducting material. However, such a connection of the shieldings via, for example, a thermally conductive rubber entails a relatively high degree of effort in terms of mounting and requires tight tolerances of the components so that excessively differing distances between the two shieldings have to be bridged. Furthermore, the resulting thermal conduction is often inadequate because the heat must first pass from the one shielding into the thermal conductive rubber and then from the thermally conductive rubber into the other shielding before the outer shielding can emit the heat into the ambient air.
The object of the present invention is to provide a shielded electronic circuit having an outer shielding and an inner shielding such that the heat passing into the inner shielding is conducted away to the outside of the electronic circuit in an optimal way without requiring a highly precise fabrication of the circuit or a complicated mounting.
The object of the present invention is met by providing an outer shielding arranged for resting on an inner shielding and having an opening in the vicinity of the inner shielding.
The configuration of the outer shielding eliminates the actual cause of the problem of poor cooling of the inner shielding, namely the enclosure of the electronic component within the inner shielding by two walls. The inventive opening in the outer shielding allows the inner shielding in the vicinity of the opening to form a part of the wall face of the outer shielding. For this reason, heat from the inner shielding is emitted directly to the outside. Accordingly, the transmission of heat out of the inner shielding into the outer shielding is no longer required.
In practice, considerable fluctuations in the distance between the inner shielding and the outer shielding are possible due to manufacturing tolerances. Accordingly, a compensation for the manufacturing tolerance is required. The compensation is easily realized in one embodiment of the present invention by arranging a plurality of spring tongues arranged next to each other on the outer shielding such that they bound the opening of the outer shielding. The spring tongues are arranged so that they rest under tension on the inner shielding.
To properly shield a component, the gaps between the outer shielding and the inner shielding have to be dimensioned with regard to the wave lengths of the interfering frequencies. This causes difficulties because it is not possible to predict accurately with which regions the outer shielding will rest on the inner shielding. These uncertainties are avoided by arranging spherical impressions on the outer shielding such that the outer shielding rests on the inner shielding along the edge of the opening via the spherical impressions and the distances of the spherical impressions are matched to the wave lengths of the interfering frequencies.
In a further embodiment, the spherical impressions are arranged on the plural spring tongues.
The spring tongues are capable of compensating particularly large differences in the distance if, according to a further embodiment of the present invention, the spring tongues are bent so as to extend in a Z-shape to compensate different relative vertical positions of the inner and outer shieldings.
A particularly good cooling effect and at the same time an overall volume which is as small as possible is obtained if the inner shielding is higher than the outer shielding relative to a main printed circuit board of the electronic circuit and the Z-shaped tongues of the outer shielding are led upward out of the plane of the outer shielding to the plane of the inner shielding.
The electronic circuit is configured optimally as a whole if the outer shielding is mounted on the main printed circuit board, a daughter printed circuit board is fitted within the outer shielding which extends parallel to and at a distance from the main printed circuit board and is fitted with at least one further electronic component, and the inner shielding is mounted on the auxiliary printed circuit board.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.